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Sealing 740 engine valve cover
Posted by: Marksteamnz (IP Logged)
Date: June 23, 2016 08:32AM

I had heard horror stories about undoing the round valve cover on the bottom of an engine,so was pleasantly suprised it came undone really easily. Looks like engine oil ran down the threads and some one had fitted an oring to seal the cover. The o ring had of course disintegrated which may be why it was easy to undo.
Anyway now I want to put the cover back on the right way.
Any suggestions ie a copper gasket? sealant?(like to avoid that) and if anyone has a number the torque setting.
Cheers
Mark

Re: Sealing 740 engine valve cover
Posted by: Rolly (IP Logged)
Date: June 23, 2016 02:24PM

Mark
Like the cylinder head there should be an undercut just below the lip of the cover for one ring of packing.
The first time I looked at a removed head the packing was so smooth it looked like part of the casting. I had to take a prick punch to dig into the packing to remove it.
I think a high temperature silicon O-ring would work just fine, you can get them good for 600 F
Rolly

Attachments: cylinder head-3.jpg (66KB)  
Re: Sealing 740 engine valve cover
Posted by: Marksteamnz (IP Logged)
Date: June 24, 2016 07:29AM

Many thanks Rolly,you absolutely nailed it, there was indeed a very dead brittle o ring turned into a triangle in the recess. I will chase up a high temp silicone replacement on Monday.
Thanks once again
Mark.

Re: Sealing 740 engine valve cover
Posted by: Rolly (IP Logged)
Date: June 24, 2016 02:17PM

Mark
McMaster-Carr list some but I canít find the correct size.
[www.mcmaster.com]
[www.mcmaster.com]
[www.mcmaster.com]
The original stuff was graphite packing. You might want to stick with it.
Rolly

Re: Sealing 740 engine valve cover
Posted by: Marksteamnz (IP Logged)
Date: July 08, 2016 10:53AM

Thanks Rolly. A local company had a viton G110V seal 3.1mm dia 109mm ID. It's a fluro polymer japanese spec with a similar heat rating to silicon. Installed and back on the engine.
One small step forward.
Thanks once again
Mark

Re: Sealing 740 engine valve cover
Posted by: Rolly (IP Logged)
Date: July 09, 2016 02:18PM

I donít see that Viton is rated much above 400F
Some products like PTFE and Silicon are rated 600F in an oxygen environment but when not in an oxygen environment they are rated much higher. PTFE can go as high as 2500F
The valve cover will get to whatever your superheat is. That can easily see 700 F if youíre not careful.
Rolly



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